Syrian opposition leaders have regularly argued that extremists are a minority within their ranks.
Kerry said this week that 15-25 percent of the rebels are extremists. "I just don't agree that a majority are al-Qaida and the bad guys," he said. "That's not true."
But Rep. Michael McCaul, R-Texas, said he didn't buy that figure, arguing that most of the Syrian opposition are radical Islamists. "Who are the rebel forces?" he asked Kerry. "I ask all the time in my briefings, and the answers get worse and worse."
And how strong the extremists are also depends on what part of the country you look at. Islamist militia are widely believed to have dominant control in rebel-held areas in northern and eastern Syria.
16. They've been accused of using chemical weapons, too.
In May, a U.N. official said evidence pointed to the use of the deadly nerve agent sarin by Syrian rebel forces. Carla Del Ponte, the commissioner of the U.N. Independent International Commission of Inquiry for Syria, told an Italian-Swiss TV station that the findings come after interviews with doctors and Syrian victims now in neighboring countries.
But the commission later issued a news release saying it "has not reached conclusive findings as to the use of chemical weapons in Syria by any parties to the conflict."
17. Human rights groups warn that Syrian rebels have also committed abuses.
Al-Assad's regime isn't the only one facing criticism from human rights groups over its record. Rebels have also been accused of possibly committing war crimes.
"Armed opposition groups too have committed serious abuses, including summary killing and torturing captured security forces, militia members and suspected informers," Amnesty International said in a March report.
Human Rights Watch called last year for opposition leaders to make it clear that kidnapping, torture and executions are unacceptable. "The Syrian government's brutal tactics cannot justify abuses by armed opposition groups," the organization said.
18. Some disturbing videos purporting to show the rebels' brutality have surfaced online.
A video posted online in May purported to show a well-known rebel fighter carving out a government soldier's heart, prompting the U.N.'s human rights chief to call for the "atrocious act" to be investigated as a potential war crime.
On Thursday, concerns over rebels' human rights record surged after The New York Times published a video showing armed rebels getting ready to execute seven captured government soldiers and throwing their bodies into an unmarked mass grave. The newspaper said the video was recorded in the spring of 2012
19. At first, the United States said it would only give the rebels "non-lethal support," like communications equipment, food and medical supplies.
Officials said that was a way to help the rebels in their fight.
It was also an effort to hem in radical Islamist groups vying for influence in Syria after the fall of al-Assad, a senior State Department official told CNN earlier this year.
20. In June, the United States pledged to give the rebels weapons.
The United States said it would send the rebels small arms, ammunition and potentially anti-tank weapons. Rebels have said they never received those weapons.
And some activists worry that whatever the United States may do in Syria, it's too little, too late.
"The international community is so late in reaction...any action cannot be correct right now," Syrian activist Zaidoun told CNN's AC360 this week. "It's too late for anything. I don't know whether we can survive."